An input device is an important part of many portable electronic devices and it is used to control operation and input information to the electronic device. In portable electronic devices such as computers, communication devices, measuring devices and similar devices the most common input devices used are keypads, keyboards and touch panels consisting of individually pressable or touchable numeric or alphanumeric, function and control keys. To activate these kind of input devices a user must press or touch a certain key or a certain touch point to accomplish a desired operation.
A known structural arrangement is to build up a keypad system on a printed wired board (PWB) with a number of contact pads on its upper surface. In this description the printed wired board (PWB) is used as an general designation for both the printed circuit board (PCB) and the PWB. The actual key switches are located on the PWB at the points where conductive input rows and conductive output columns form a junction, i.e. a key switch, comprising a conductive dome. An insulating film covers the PWB except of those contact pads onto which components are to be placed. The keypad part comprises a dome sheet or alternatively a selection of individual key domes made of some resilient material that is electrically conductive at least at the concave surface of each dome. Additionally the keypad part comprises a rubbery keymat where the bulging protrusions coincide with the conductive domes of the dome sheet and constitute the visible parts of the keys. Pressing the key will cause the conductive dome to produce an electrical contact at the key switch.
In portable electronic devices such as mobile phones, communicators and laptops the keypad arrangement is built on the “engine PWB”. The engine PWB is a common designator of such printed wired boards that comprise a remarkable number of electronic components that implement the main functionalities of the telecommunication device. The electronic part of the portable device, the engine PWB being part of this electronic module, is usually encapsulated so that it is shielded against electromagnetic interference and other disturbances. Thus the electronic part constitutes its own entity which is then enclosed in the outer casing forming the cover part of the portable device. The rubbery keymat with bulging protrusions constitutes one side of the electronic part of the portable device and this side will abut on the cover part with openings fixed for bulging protrusions. The electronic part and cover part is then anchored to each other with fasteners.
Today manufacturing processes for keypad arrangements and cover parts of portable devices are totally different and are commonly performed even in separate manufacturing facilities by different providers or sub-contractors. The keypad arrangement including circuitry, electronic components and sheet material components is manufactured by conventional PWB manufacturing processes including screen printing, component assembling and reflow soldering. The cover part is generally manufactured by engineering plastic moulding processes.
A printed wired board (PWB) or a printed wiring board is a rigid support with connections in the form of flat metal strips. Typically the connections are “printed” as a pattern of lines of etch-resist ink over a uniform metal coating on the board. Etching removes the unmasked regions, leaving the interconnect lines. The etch-resist is then also washed off, leaving the wires exposed and available for connection. At the ends of the lines, holes may be drilled to allow the leads of surface components or sockets to be passed through. Discrete components like resistors and power transistors are inserted directly. Microchips and the like are soldered on directly or sockets are soldered onto the board where these active components are then inserted.
Exchangeable covers have gained popularity especially among young consumers who want visually-differentiated cover parts to their portable electronic devices. The cover part can be decorated using so called in mould decoration (IMD) processes which are gaining ground nowadays. This technique consists of the decoration of an injection moulded part during the moulding process. A special carrier film or foil, which is also called in mould decoration (IMD) foil or customized injection mould (CIM) foil, is used to forge the decoration to the cover part. In the IMD process a flat piece of film or foil is first decorated with desired texts, patterns, images, pictures or alike layouts and then the film is formed to fit the profile of the injection mould and cut to shape. After that the film is inserted as an insert into a mould cavity, where finally moulding resin is injected onto the back of the film. The resin fuses onto the back of the film, and the materials are bonded together. The cover part is now complete and no postprocessing is required. As high temperature moulding resins typically polycarbonate, ABS and blends are used. ABS is an acronym for acrylonitrile-butadiene-styrene copolymers, which are elastomer-modified styrene plastics (thermoplastic). For example, key caps and buttons made of pre-printed foil can be implemented in the cover parts formed from in-coloured co-extruded film using IMD process.
Today, high pressure formed decorative printed foil keypads with back injection moulded taps using IMD technology are widely used in electronics and this same technology is also used in cover part manufacturing. These keypads and covers need a separate printed wired board for user interface connections, tactile feed back and other electronic functionality, which separate PWB is physically locating in connection with the electronic part of the portable device.
The need for miniaturization of portable electronic devices sets limits to the size of the electronic part comprising the engine PWB which is a reason why the engine PWB is used as an electronic platform for keypad arrangements. This means that the keypad arrangement and the engine PWB layout is fixed to each other and it will be difficult to change the keypad layout without changing the engine PWB. This kind of keypad arrangement limits a lot the freedom to design differentiated keypad layouts to exchangeable cover parts of the portable electronic devices.
In view of various inherent limitations of integrating keypad arrangements flexibly to the portable electronic devices, it would be desirable to avoid or mitigate these and other problems associated with prior art arrangements. Thus, there is a need for new techniques to provide electronics-mechanics integration for electronic devices.